First timer

I'm on CD 36 (normally 31)... DPO 19days...AF late by 4days... I did the early detection test 6days before my period was due which was Saturday and was a BFN then did another one on Saturday and again BFN... Just curious if there's still a chance there could be a positive since I'm 4days late and when to test again if I don't get it .. which I hope I don't. 🤞